The problems associated with the antigens specified above become clear when, for example, it is desired to make monoclonal antibodies against the specificity determining part of a T-cell receptor (TCR). Such (monoclonal) antibodies are known as anti-clonotype antibodies as they recognize the antigen-specific part (or clonotype structure) of a T-cell receptor of one particular T-cell clone. While (murine) monoclonal anti-clonotype antibodies against murine T-cell receptors (TCR) have been reported only occasionally, there are even less (murine) monoclonal anti-clonotype antibodies known against human T-cell receptors. T-cells are hard to culture, making it difficult to obtain and purify a sufficient amount of antigen, i.e. T-cell receptor protein. This in turn makes it difficult to obtain an immune response and also makes screening difficult. In one of the few cases where a monoclonal anti-clonotype antibody is available against a human TCR, these problems did not arise because the antigen was present on Jurkat leukaemia cells (ref. 1). As leukaemia cells can be cultured in unlimited amounts, the problem of a shortage of antigen did not arise. Therefore, until now no method was available to prepare monoclonal antibodies against rare and/or very unstable antigens without having to screen unfavourably large numbers of hybridoma clones.